A TOOL FOR USE IN GLASS MANUFACTURE

Abstract: A tool for use in glass manufacture, such as a glass mould, plunger or the like, having at least a portion of the surface of the tool provided with a layer produced by a suitable coating method, the layer consisting mainly of a manganese-containing nickel aluminide, the strength properties of which increase as a function of temperature from room temperature to at least 450 DEG C. An inherent feature of the manganese-containing nickel aluminide is that the oxide layer forming on the surface of the tool does not substantially increase after the primary forming of the layer and that the quality of the surface of the surface layer improves in the operational temperatures of the glass mould under the influence of molten glass when compared to the quality after the machining of the surface, i.e. the compound possesses a self-polishing feature.

Description: A TOOL FOR USE IN GLASS MANUFACTURE The present invention relates to a tool for use in glass manufacture, such as a glass mould, plunger, or the like, in which at least part of the. surface is provided with a layer produced by means of thermic spraying, e.g. plasma spraying, detonation spraying, hypersonic flame spraying, sputtering or other suitable method of coating or in which tool the whole tool or a part thereof is made of the same material as the surface layer utilizing a suitable method, and in which the surface layer of the tool comprises at least one inter- metallic composition, the strength properties of which increase as a function of temperature from room temperature to a temperature of at least 450 °C. When mass producing, for example, glass packings, such as bottles, the molten glass is formed into the product by means of a suitable mould, in which the molten glass is formed either by a plunger or by combination of gas pressure and under-pressure subsequent to which the glass solidifies into the form. The process of forming the molten glass can comprise several phases. During the first phases the molten glass must be capable of moving on the surface of the mould, whereby the friction forces between the molten glass and the mould determine the quality of the product. Great friction forces mean that the glass does not solidify simultaneously at all places in the mould, whereby the product glass is wavy and contains micro-cracks. In principle the problem can be avoided by increasing the temperature of the molten glass, thus decreasing the viscosity and increasing the fluidity of the molten glass. The problem with increasing the temperature is that in high temperatures the molten glass starts to stick to the surface of the mould. Nowadays the temperature of the mould during manufacture of glass is about 500°C, which makes it possible to use cast iron moulds. In order to decrease friction and to improve the quality of the product the mould is nowadays painted with a graphite- based paint and lubricated with graphite grease. The durability of the paint is about 2-8 hours and the mould must be lubricated about every 15 minutes. The lubrication is associated with considerable generation of smoke and smells. When a high rate of production is the aim, another important factor is heat transfer from the molten glass to the mould and further to a cooling medium. The desirable high production rates demand that the "transition resistance" between the molten glass and the mould be as small as possible. In the heat transfer chain from glass to cooling air the "smallest gate" is the transfer of heat from the mould to air. Within the glass, heat convection resistance is relatively greater, but in the forming process the glass must be maintained in forming viscosity until final blowing. From the standpoint of glass cooling, changing the mould material is not too effective a measure. The heat resistance in the transition region between the glass and mould is larger than in the mould itself. That is due to unevenness of the surface and the air remaining between the mould and glass. The heat transfer varies considerably as a function of time. In the beginning of the contact the heat transfer is very effective, but it slows rapidly when the temperature gradient decreases and when heat convection inside the glass limits the heat stream. The temperature of the outer surface of the mould does usually not vary as a function of time. The thickness of the wall of usual glass packing products is of the order of 2-3 mm, regardless of the size of the packing. The ratio of the weight of the packing to the area of its outer surface is also of the same order. On the outer side of the mould the heat transfer is mainly effected by convection, i.e. the possibility of improving cooling is connected to an increase in the speed of the cooling air or to increasing the heat transfer area by means of fins. An even more efficient cooling can be accomplished by using water or water mist for cooling instead of air. This, nevertheless, creates new problems by causing rusting of the machinery and moulds. These problems can be overcome by choosing appropriate materials for the moulds or by coating the existing surfaces with suitable materials, but these solutions require considerable investments. When the cooling effect increases on the outside of the mould, it causes a larger temperature gradient between the inside and the outside of the mould. If air cooling is utilized, the temperature of the outside of the mould does not decrease to any considerable degree, whereby the inside temperature of the mould increases. This can be avoided by replacing the mould material with a more heat conductive material. This, nevertheless, again contradicts with cost-effectiveness. Air pores remain between the mould and the glass, as was stated earlier. The amount of air pores between the mould and glass depends on the evenness of the surface, the contact temperature, mould material and the properties of glass. Where the glass contacts the mould, heat is transferred by convection, and in the pores the heat is transferred by radiation and convection via air. All the modes of heat transfer are in direct proportion to the heat transfer area, whereby a change in the heat transfer area has an effect on heat transfer. Were the most efficient heat transfer evenness grade, a relatively rough surface of about 20 μm, to be used, a relatively great amount of micro-cracks would be caused in the surface of the end product. Therefore, it is desirable to try to achieve as even a surface as possible on the surface of the final mould, whereby both a good heat transfer density and a minimization of micro-cracks is achieved. Elevating the contact temperature also improves the heat transfer (the softer glass fills any unevenness in the mould surface) and, simultaneously, the amount of micro-cracks is reduced on the surface. In an elevated temperature the glass has a tendency to stick on the surface of the mould. The factors having an effect on the sticking temperature are the mould material, the viscosity of glass, the evenness of the mould surface and the pressure of glass against the mould. The different mould materials' tendency to stick depends on the surface tension of each material. Surface tensions of metals are of the order of 1.7 - 1.0 x 10 "2 N/cm. The unevenness of the surface has an effect on sticking via heat transfer, i.e. the glass cools unevenly on its surface against a suitably rough surface, and these cold spots prevent the glass from sticking in the mould. They, nevertheless, simultaneously cause micro-cracks on the surface of the glass, as was stated above. The present invention relates to minimizing the above-mentioned disadvantages, partly even eliminating them, and to enhanced ability of controlling the cooling of the glass product under manufacture, as well as the strength properties of the product by improving the surface quality of the product. This is achieved by means of a tool, the surface layer of which comprises at least one intermetallic compound, a characteristic feature of which is that the oxide layer forming on the surface of the tool does not substantially increase after its primary formation. In this context, the term "machining" is used to describe all the measures needed to achieve the final finish of the surface of the glass mould. Thereby, all different polishing methods, for example, fall under the term "machining" in this context. When the research on and search for solutions for the above-mentioned problems was started, one natural alternative was that the tool materials be coated with a suitable coating material or, in special applications, the whole tool or a part thereof be manufactured from the coating material. Undesirable sticking problems and peeling of the coating material can be avoided, when the whole tool or a part thereof is, in some critical applications, manufactured from the same material as the coating in, e.g., easier partial mould applications. When different coating materials were assessed, the first alternatives were naturally different ceramic coating materials and some commercially widely used super-alloy coatings. The disadvantages of ceramic compounds are e.g. porousity and poor heat transfer properties. Also, a poor tolerance of heat shocks is a common drawback of these coatings. Another disadvantage of these coatings is their lack of easy machinability and an especial disadvantage of these coatings is that the surface of the mould can not be easily polished. Various nickel- or cobalt-based super alloys have yielded good, or, rather, expected results in tests. Thus, the resultant properties of end products were not such as to awaken hopes about a considerably improved tool for glass manufacture. Thus, a mere coating as such did not offer a good solution for the present problems. In coating experiments some materials, namely intermetallic compounds, known per se, but still relatively new as construction materials, were experimented with, and these materials offered unexpected advantages. It has previously not been worthwhile to use intermetallic compounds as construction materials because of the brittleness of the compounds. It was not until the effect of certain additives, such as boron, in increasing tensile properties was noted, that intermetallic compounds have been available for construction purposes, i.e. both as coatings and as solid material. A surprising observation during experimentation was that some intermetallic compounds had quite a high sticking temperature for glass. A typical feature of some of the intermetallic compounds is that their strength properties increase until a certain limit when temperature is elevated from room temperature to higher temperatures. Hardness, for example, can double during the transition from room temperature to 500° C. Certain intermetallic compounds, after a suitable alloying, are capable of increasing their strength properties even up to temperatures of about 800°C. In room temperature these modified compounds are relatively soft and thus easily machinable and polishable, an essentially important factor when choosing the material for glass manufacture moulds. An inherent feature of intermetallic compounds is their good thermal conductivity. When the base material of the mould, usually cast iron, is coated with an intermetallic compound and then carefully polished, it is possible to considerably decrease the formation of micro-cracks in the glass product. It is, nevertheless, advisable in some critical stages to be prepared to manufacture a part of the tool, such as a part of the mould or the whole mould, of the same material as the coating, but as solid material. Thus the risk of peeling or problems with sticking can be avoided. By means of a suitable coating material, be the coating either a coated layer or a part of the solid material surface, it is possible to decrease the wall thicknesses of glass products and thus produce lighter glassware with as good a strength as glassware produced by previous methods having thicker walls. When good machining properties are combined with increasing strength, thereby also hardness, i.e. overall durability, with temperature elevation from room temperature to normal operating temperature, e.g., 500 - 650°C, it is clear that this kind of material is extremely suitable for use as surface material in glass manufacture tools. The strength of a suitable intermetallic compound will increase from room temperature to at least a temperature of 450°C. The properties of these compounds can be improved by suitably alloying them whereby their room temperature tensile properties are considerably improved and/or the increase in strength properties can be continued up to about 800°C. These alloying elements include boron, (increases room temperature tensile properties) and hafnium (continues improving strength properties into higher temperatures). Iron, titanium, manganese, zirconium, cerium and niobium can also be used as alloying elements for improving the properties of intermetallic compounds. Usually, the quality of the surface of the glass manufacture tool, such as a mould, is at its best when new, i.e. directly after machining as defined above. The tendency of the molten glass to stick on the surface of the tool is at a minimum when the surface of the mould is suitably oxidized. Nevertheless, various lubricants have to be regularly used during production with known glass tool surface and/or coating materials in order to avoid the molten glass sticking to the mould surface. The optimum thickness of this oxide layer is achieved in about 24 hrs of production with conventional coatings. After this, the oxide layer both increases in thickness, gets brittle and tends to flake off the surface during further production. The increase in thickness is due to the diffusion of oxygen through the oxide layer towards the metal and the diffusion of metal through the oxide layer towards the free surface. Thus, the oxide layer has a tendency to flake off during production and flakes of it stick onto the surface of the glass, thereby causing a deterioration in the quality of the surface of the glass, and, subsequently, deteriorating the strength of the glass. These flakes are formed by both the loosening layer of oxides and the lubricants used during production. So, it is necessary to periodically clean the mould by means of, e.g. sand blasting to remove the irregularly stuck lubricant and oxide layer. After sand blasting, it is naturally necessary to polish the surface of the mould prior to using the mould again. This leads to the initial position, and the same cycle goes on for as long as it is necessary to finally replace the mould. In a test run utilizing different aluminides as the intermetallic compounds forming the surface layer of the glass bottle mould, a surprising fact was noted, concerning especially manganese-containing nickel aluminides. When such a mould was taken into use for manufacturing glass bottles, it was completely unexpectedly observed that the quality of the surface of the plunger of the glass mould started to improve after about half an hour of production run. When the production was interrupted, the surface of the mould was observed to be in better polish than when unused, i.e. directly after the manufacture of the mould. Thus, this means that the quality of the surface of the bottles and thereby also their strength properties, especially their impact strength were improved during the production run, instead of decreasing, as one could suppose. The oxide layer forming the surface layer was also very dense and thin, so that it had not substantially increased in diameter subsequent to its primary formation. This self-polished and oxidized surface layer substantially contained mixed oxides of manganese and aluminum. These nickel aluminides having a compound of the type Ni 3 (Al+Mn)+B have, due to their peculiar self-polishing feature and the advantages caused by it, been found to easily better the rest of the known surface coating materials as surface and/or surface coating materials. A characterizing feature of all previously known surface coating materials is that the quality of the surface decreases right from the startup until the moulds have to be changed. Also, the constant need for lubrication and the flaking off of the oxide layer add to the negative features connected with the known surface and/or surface coating materials. The surface materials according to the invention enable the sticking temperature of glass to be raised from a value typical to optimal cast iron, 500-540°C, all the way to temperatures of 550-630°C, while achieving very good surface qualities of the glass mould, which leads to good surface properties of the product. The surface properties even improved during the initial stages of the production. By utilizing the solution according to the invention, the detrimental flaking of the surface, found in connection with conventional surface and/or coating materials, can be avoided. Due to the invention, the consumption of lubricants has been substantially reduced when compared to the consumption of known surface and/or coating materials in the same operation temperatures. The exact reason for this improvement of properties (thin, dense oxide layer and self- polishing) of the surface of the tool has not yet been found, but it is likely to be because of the interactivity caused by the chemical and physical properties of the surface and/or coating material according to the invention and related to both the relatively high operating temperature of the glass mould and the chemical and mechanical properties of the molten glass. The coatings can be produced by a variety a methods, such as plasma spraying, detonation spraying, hypersonic flame spraying, sputtering or other suitable method. Various known methods can also be used for manufacturing the moulds from solid material. The solution according to the invention can be applied within the inventive scope defined in the appended claims.

Claims: WE CLAIM: 1. A tool used in glass manufacture, such as a glass mould, plunger or the like, in which at least a portion of the surfaces of the tool is coated by means of thermic spraying, such as plasma spraying, detonation spraying, hypersonic flame spraying or sputtering or other suitable coating method with a surface layer or in which tool the whole tool or a part thereof is manufactured from the same material as the surface layer by means of a suitable method, the surface layer of the tool mainly consisting of at least one intermetallic compound, the strength properties of which increase as a function of temperature from room temperature to a temperature of at least 450°C, characterized in that an inherent feature of the compound is that the oxide layer forming on the surface of the tool does not substantially increase after its primary forming. 2. A tool according to claim 1, characterized in that another inherent feature of the inter-metallic compound is that the quality of the surface layer of the tool improves under the influence of molten glass when compared to the quality after the machining of the surface, i.e. the compound possesses a self-polishing feature. 3. A tool according to claims 1 or 2, characterized in that the surface layer mainly consists of manganese-containing nickel aluminide. 4. A tool according to claims 1, 2 or 3, characterized in that the self-polished and oxidized surface layer of the tool substantially consists of mixed oxides of aluminum and manganese, whereby the oxide layer forming on the surface of the tool is very dense and resistant against the so-called flaking of the surface during operation. 5. A tool according to claim 4, characterized in that the surface layer mainly consists of nickel aluminide of the type Ni 3 (Al+Mn)+B.

Inventors: MAENTYLAE TAPIO, REUHKALA PAULI, TIAINEN TUOMO, MAENTYLAE, TAPIO, REUHKALA, PAULI, TIAINEN, TUOMO
Applicants: AHLSTROEM RIIHIMAEEN LASI OY, HACKMAN DESIGNOR OY AB, MAENTYLAE TAPIO, REUHKALA PAULI, TIAINEN TUOMO, MAENTYLAE, TAPIO, REUHKALA, PAULI, TIAINEN, TUOMO
Application year: 1994
Main classification: C03B9
IPC codes: C03B9, C03B40, C23C4, C23C14, C23C30